The Infernal Architect

Reincarnated into his past self, Tyler is given the chance to correct his biggest mistake. He rediscovers the Liber Infernus- an ancient tome penned by a fallen celestial.
[By wielding this book, you gain access to the lost knowledge and inventions and oblige to being the new infernal architect! However, the price you must pay is your humanity. You must accept to turn into a demon and brace all its downsides. Do you consent?]

Tyler stared calmly at the book as a smirk silently rose on his lips.
"Yes!"
Just that simple word was enough to change his fate for the better and stop the impending apocalypse from ever happening. Or was it?

His fate will change, alright. But for the better? - I highly doubt that!